There is known a fixing device including a heat member that applies heat to a recording sheet, a pressure roller that forms a nip portion between the pressure roller and the heat member, an urging mechanism that urges the heat member to the pressure roller, and a change member that changes the width of the nip portion by applying a pressing force to the heat member against an urging force of the urging mechanism. With this technique, the change member can change the width of the nip portion to a first nip width for thermal fixing or a second nip width (0) for jamming processing. The second nip width is smaller than the first nip width.
With this technique, the urging mechanism has a structure including an arm member that can swing while supporting the heat member, and an urging member that urges the heat member to the pressure roller through the arm member. The change member includes a cam that presses the arm member against an urging force of the urging member. Additionally, when the cam is released from the arm member, and hence the movement of the arm member is no longer restricted by the other member such as the cam, the entire urging force of the urging member is applied to the pressure roller. As a result, the width of the nip portion becomes the first nip width. When the cam presses the arm member against the urging force and receives the urging force, the width of the nip portion becomes the second nip width.
However, with the technique of the related art, for example, if the hardness of the pressure roller changes with use, e.g., due to the pressure roller receiving an entire urging force when the width of the nip portion is the first nip width, the nip width may become a nip width larger than the maximum value of an allowable range for the first nip width. In this case, proper fixing performance may not be achieved.